The invention is related to hydraulic systems, and in particular, to a multi-function hydraulic valve assembly.
The use of hydraulic systems for moving or lifting loads is well known. Typically, such systems utilize hydraulic fluid under pressure to drive hydraulic operators, such as piston/cylinder arrangements. A piece of machinery, such as a hoist or a truck, may require several hydraulic operators to move the load in different ways. Typically, the various hydraulic operators are each controlled by a lever located in the cab of the machine or vehicle. One example where hydraulic systems are used in this way are lift trucks.
Lift trucks are vehicles which are used to pick up and move loads from place to place. A conventional lift truck includes a carriage which supports a pair of forks. The forks are maneuvered into place by the lift truck operator and are used to pick up the load. The carriage rides vertically in a mast, which also supports the carriage. In addition the mast may be tilted backward to facilitate stabilizing the load on the forks. Two separate hydraulic operators are used to move the carriage vertically and to tilt the mast.
Several attachments to enhance the capabilities of the lift truck are known in the art. One such attachment is a side shift assembly which facilitates aligning the spaced pair of forks with the load. The term xe2x80x9cside shiftingxe2x80x9d is used to describe the concept of shifting the forks as a spaced pair either left or right of the vehicle center line. This function provides the operator with a greater margin for error when aligning the vehicle with the load. A hydraulic operator, such as a piston/cylinder arrangement is typically used by the side shifting assembly to move a frame to which the forks are secured.
Another attachment to enhance the capability of a lift truck is a fork positioning assembly. The term fork positioning is used to describe the concept of changing the relative spacing between the forks to accommodate loads of different widths. Again, a hydraulic operator, such as a piston/cylinder arrangement is used in the fork positioning assembly to move the forks.
A cab of a conventional lift truck provides three levers to operate three hydraulic operators. Accordingly, if a user requires four hydraulic operators, such as, for example, by installing a fork positioning attachment, an additional lever must be installed to operate the fork positioning attachment.
Alternatively, prior art systems permit operation of two separate hydraulic operators with a single lever on a lift truck. These systems utilize an electrical circuit to toggle between the two hydraulic operators. Prior to moving the lever which actuates the hydraulic system, the user would activate the electrical switch to select the appropriate hydraulic operator. This system adds expense and complexity to the design of the lift truck. In addition, electrical cables must be provided and extended over the lift truck mast.
Accordingly, there is a need for a hydraulic valve assembly which permits selectable hydraulic operation of more than one hydraulic operator with a single lever.
According to a first aspect of the invention, a hydraulic valve assembly for delivering hydraulic fluid from a supply of hydraulic fluid to one of a first hydraulic operator and a second hydraulic operator is provided. The assembly comprises:
a) a valve block defining:
i) a first supply port adapted for fluid communication with said supply;
ii) a second supply port adapted for fluid communication with said supply;
iii) a first operator port adapted for fluid communication with said first hydraulic operator;
iv) a second operator port adapted for fluid communication with said second hydraulic operator;
v) a third operator port adapted for fluid communication with said first hydraulic operator;
vi) a fourth operator port adapted for fluid communication with said second hydraulic operator;
vii) a first chamber, said first chamber being in fluid communication with said first supply port, said first operator port, and said second operator port;
viii) a second chamber, said second chamber being in fluid communication with said second supply port, said third operator port and said fourth operator port;
b) a first selection valve located in said first chamber and a second selection valve located in said second chamber, said first and second selection valves being adapted to move in unison, said first and second selection valves operable between a first position when said hydraulic fluid is at a first pressure and a second position when said hydraulic fluid is at a second pressure, where in said first position, said first selection valve permits fluid communication between said first supply port and said first operator port, and said second selection valve permits fluid communication between said second supply port and said third operator port, where, in said second position, said first selection valve permits fluid communication between said first supply port and said second operator port, and said second selection valve permits fluid communication between said second supply port and said fourth operator port; wherein said first pressure is lower than said second pressure.
According to a second aspect of the invention, a hydraulic valve assembly for delivering hydraulic fluid from a supply of hydraulic fluid to one of a first hydraulic operator and a second hydraulic operator is provided. The assembly comprises:
a) a valve block defining:
i) a supply port adapted for fluid communication with said supply;
ii) a first operator port adapted for fluid communication with said first hydraulic operator;
iii) a second operator port adapted for fluid communication with said second hydraulic operator;
iv) a chamber, said chamber being in fluid communication with said supply port, said first operator port, and said second operator port;
b) a selection valve located in said chamber, said selection valve operable between a first position when said hydraulic fluid is at a first pressure and a second position when said hydraulic fluid is at said second pressure, where in said first position, said selection valve permits fluid communication between said supply port and said first operator port, where in said second position, said first selection valve permits fluid communication between said supply port and said second operator port; wherein said first pressure is lower than said second pressure.